Liquid sensor for reciprocating refrigerant compressor

ABSTRACT

Method and means for preventing operation of a reciprocating refrigerant compressor in the event that there is liquid at the inlet to the valve mechanism in such compressor.

United States Patent 11 1 Parker Oct. 23, 1973 [54] LIQUID SENSOR FOR RECIPROCATING 2,534,455 12 1950 Koontz 62/226 REFRIGERANT COMPRESSOR 2,871,673 2/1959 Richards. 62/83 .2- m2 2- 3,232,519 2/1966 Long 417/13 Inventor: sldlley Parker, Fort Worth, 3,290,576 12 1966 Jensen 318/471 Tex. 3,411,313 11/1968 Brown 417/13 [73] Assignee: Lennox Industries Inc., Marshalltown Iowa Primary ExaminerW1111am J. Wye [22] Flled' 1972 Attorney-A. W. Molinare et a1. [21] App]. No.: 215,752

[52] U.S. Cl 62/226, 62/83, 62/129, [57] ABSTRACT Method m n for reventing o eration of a re- [58] Field of Search 62/84, 83, 129, 190, ciprocating refrigerant compressor in the event that 62/192 471; 417/131 279 1 there is liquid at the inlet to the valve mechanism in such compressor. [56] References Cited UNITED STATES PATENTS Turner 62/226 5 Claims, 2 Drawing Figures LIQUID SENSOR FOR RECIPROCATING REFRIGERANT COMPRESSOR BACKGROUND OF THE INVENTION This invention relates to an improved refrigerant compressor and more particularly to improved means and method for controlling operation of a reciprocating refrigerant compressor to prevent actuation of the compressor in the event there is an undesirable quantity of incompressible fluid (liquid) at the inlet to the valve mechanism in such compressor in order to prevent damage to the valve mechanism. 7

A serious problem causing valve breakage and damage in reciprocating refrigerant compressors is the slugging condition at start-up which results when liquid rather than gas enters the valve mechanism. Such liquid may be lubricant (oil), refrigerant, or combinations of the named liquids. Basically, a refrigeration system is comprised of a compressor, a first heat exchanger or condenser, expansion means and a second heat exchanger or evaporator. Refrigerant gas is compressed in the compressor and the high pressure vaporous refrigerant passes through a discharge line to the condenser where it is condensed. The flow of refrigerant from the condenser to the evaporator is controlled by the expansion means which may be either a capillary tube or a thermal expansion valve. Expanding gas in the evaporator absorbs heat and the medium passing over the evaporator (air or water) is cooled. The refrigerant gas flows back to-the compressor through the suction line.

A lubricant sump is commonly provided within the reciporcating refrigerant compressor. Lubricant is migrate-to'the compressor.- Primarly, three factors de-- termine the rate at which refrigerant is absorbed in the oil. One is the vapor pressure differential at a stabilized temperature which causes a driving force forcing the refrigerant vapor in the system to flow to the oilrefrigerant mixture in the compressor sump. A second factor is theactual temperature differential between the refrigerant and oi]. These factors are closely related as the vapor pressure is responsive to temperature and the vaporpressure is basically the driving force.

The greater the vapor pressure differential and the greater-the temperature differential between the refrigerant and the oil, the faster theoil will absorb the refrigerant.

A third factor is the amount of oil surface exposed to the refrigerant vapor. As the major portion of the oil in the refrigerant system is in the compressor sump, the

larger the area of the sump oil surfaces, the faster the oil will absorb refrigerant vapor. v

Attempts have been made to overcome the problem of refrigerant migration and slugging at start-up by providing heaters in the compressor-to heat the oil in the sump. The heaters are designed, to maintain a predetermined higher temperature in the compressor than in the condenser, for example, a temperature differential on the order of 30 Fahrenheit. Heating of the'oil in the compressor has been found helpful, however. such heaters have not solved the problem of valve damage due to liquid. For example, the condensing unit is sometimes placed exposed to the sun, and in the spring the sun will warm the condenser more rapidly than the compressor, with the result that notwithstanding the use of a heater in the compressor, the compressor might actually be colder than the condenser or there would be insufficient temperature differential such that refrigerant would migrate to the compressor. At startup, liquid will be present in the entrance to the vale mechanism and during the compression stroke and/or suction stroke, damage can result to the valving.

Sometimes refrigerant condenses within the refriger ant system and this may also accumulate at the entrance to the valve mechanism of the compressor. Since the liquid would be incompressible upon start-up of the compressor, it too might result in damage to the valve mechanism.

An object of the present invention is to provide improved reciprocating refrigerant compressor control means and method for preventing operation of the compressor in the event there is an undesirable quantity of liquid at the entry of the valve mechanism.

Another object of the present invention is to provide an improved method for operating a refrigerant compressor which comprises the step of preventing operation ofthe motor in the compressor in the event a predetermined quantity of liquid is sensed at the inlet to the .valve mechanism.

Yet another object of this invention is to provide a reciprocating refrigerant compressor with an improved control including a state of matter disposed adjacent to the inlet to the valve mechanism for sensing a predetermined liquid condition at such location and preventing operation of the compressor until such liquid condition is obviated. I

Yet another object of the present invention is toprovide a reciprocating refrigerant compressor having improved means -for controlling the operation thereof, such improved control means comprising a liquid sensorfor-detecting a predetermined liquid condition at the entry to the suction valving of the reciprocating compressor. Other objects and advantages of the present invention will be made more apparent hereafter.

BRIEF DESCRIPTION OF THEDRAWING There is shown in the-attached drawing a presentlypreferred embodiment of the present invention wherein:

FIG. 1 is a cross-sectional.elevation view of a reciprocating refrigerant compressor embodying principlesof the present invention, with a typical refrigeration system within which the compressor isdisposed being shown schematically; and. I FIG. 2 is a schematic wiring diagram of the control circuit for the compressor of FIG. 1. i

DETAILED DESCRIPTION OF THE PRESENT INVENTION 1 pressor l and discharged through the discharge line 11 to the condenser 12 where the high pressure vaporous refrigerant is condensed. The expansion means 14 which may be either a capillary tube or a thermal expansion valve controls the flow of refrigerant from the condenser 12 to the evaporator 16. The refrigerant is returned to the compressor from the evaporator through suction line 17. Normally, the condenser is aircooled or water-cooled in order to effect condensing of the high pressure vaporous refrigerant. Air or water passing over the evaporator would be cooled by the expansion of the refrigerant therein and would be forwarded by suitable duct or conduit to the area to be cooled.

The reciprocating refrigerant compressor 10 comprises a gas-tight outer housing or casing which includes an upper shell 22, a lower shell 24 integrally joined to one another as, for example, by welding. A plurality of legs 26 are suitably secured to the compressor 10 to support it in an upright position.

Resiliently supported within the outer housing or casing of the compressor 10 by spring means 30 is compression mechanism 32. The compression mechanism includes a compressor block 34 having defined therein cylinder means 36. The cylinder means may comprise one or more cylinders in the compressor block or may be a cylinder liner disposed'in a suitable opening in the compressor block. Movable within each cylinder means 36 is a piston 38 which is adapted to be driven from the drive shaft 40 which is actuated by power means 42. The power means 42 preferably comprise an electric motor having a stator 41 secured to the compression mechanism and a rotor 43 inductively connected to the stator 41 and fixedly secured to the drive shaft 40 to rotate same.

Provided at the end of each cylinder 36 and closing the end of each cylinder cavity is a valve assembly 46. The valve assembly includes a discharge valve 48 and a suction valve 50. The suction valve will open on the suction stroke of the piston to permit refrigerant gas (suction gas) to enter the cylinder. On the compression stroke, the suctionvalve will be closed and the discharge valve opened to permit the flow of compressed refrigerant gas to the discharge muffler in the compression mechanism and then to the discharge line for forwarding to the condenser. In the event that liquid en-' ters the cylinder on the suction stroke, there is a good likelihood that suction valve damage or breakage will occur on the discharge or compressor stroke.

A feature of this invention is the provision of a state of matter sensor 60 adjacent the entrance to the valve mechanism 46. The state of matter sensor 60 is spaced as closely as possible to the entrance of the valve mechanism 46 so as to sense the presence of a predeter' mined quantity of liquid and to prevent operation of the compressor motor in the event there is a sufficientquantity of liquid that would cause damage to the compressor valve assembly 44 upon startup. Preferably, the state of matter sensor comprises a liquid sensor and takes the form of a thermistor. The liquid sensing thermistor may be of the type made by Controls Company of America.

The specific form of state of matter sensor can be varied as, for example, a float sensor, a sonic sensor, or an optical sensing arrangement can be utilized.

There is shown in FIG. 2 a schematic wiring diagram for the compressor 10. The motor 42 is connected to lines T and T through contacts a and 70b of relay coil 70. When contacts 70a and 70b are closed, the motor will be energized. The relay coil 70 is in a series circuit called a pilot cicuit with a plurality of actuating and safety switches that are connected to lines L, and L that receive power from a suitable source, for example, a low-voltage transformer. The switches in the pilot circuit may include a thermal responsive switch 72 (normally open) that is adapted to close upon demand for cooling in an area to be cooled. The switch 74 may be a normally closed motor safety switch adapted to open if the temperature of the motor should exceed a predetermined value. Swtich 76 is the liquid sensor itself or alternatively it may be a normally closed switch actuable in response to the liquid sensor.

In operation, the switch 74 is normally closed, as is switch 76. Switch 72 is closed when there is a demand for cooling, closing the circuit through relay coil 70 to energize the coil. Contacts 70a and 70b are closed upon energization of coil 70 to energize motor 42. Should the motor temperature exceed a predetermined value, switch 74 will open to deenergize coil 70 and break the circuit to motor 42. Likewise, if sensor 60 detects liquid at the entry to the suction valving of the reciprocating compressor 10, switch 76 will be opened to deenergize the coil 70. The thermistor liquid sensor 60 has a relatively high internal resistance when immersed in liquid and a relatively low resistance when in a gaseous medium. The thermistor 60 is used to control switch 76 in series with relay coil 70 in the pilot circuit to prevent operation of the compressor motor 42 in the event an undesirable liquid quantity is in the area ofthe inlet to the compressor valve mechanism. As aforenoted, other liquid sensors can be employed in place of the thermistor-type device illustrated in which case switch 76 could be actuated through different means, for example, switch 60 might be a magnetically actu ated float switch, an optically actuated switch, or a sonic actuated switch.

It should be noted that a crankcase heater is often used to heat the lubricant in the sump of the compressor and/or the compressor block. When the heat output within the compressor is sufficient to reevaporate the liquid refrigerant,-switch 76 will again close and restore the pilot circuit to a complete circuit. Coil 70 may be energized to again close switch contacts 70a and 70b to again start the motor 42.

A unique feature of this invention is the sensing of 3 liquid condition rather than a pressure or temperature condition of the suction gas or of the oil. For example,

there is shown in the Courtney U.S. Pat. No. 2,81 1,0 l 9 a device using thermistors to sense the temperature of the suction gas returning to the compressor. However, there is not suggestion found in the patent of sensing a liquid condition at the entrance of the valve mechanism in order to prevent slugging'at start-up of the compressor. The Long U.S. Pat. No. 3,232,519 also suggests the use of a plurality of temperature sensors to sense temperature conditions within a compressor. There is no teaching in the Long patent of providing a liquid sensor to accomplish the same purpose as the present invention. Use of the Long teaching would shut down a compressor as shown in the present invention, even when it should be running. The Shaw U.S. Pat. No. 3,426,962 discloses a sensor for detecting the presence of oil in the refrigerant sump in a compressor to insure that there is adequate lubrication. The gist of this patent is unlike that of the present invention. The present invention is unique in that it senses the presence of liquid in the area adjacent the inlet to the suction valve in the compressor to prevent primary slugging of refrigerant. There is no suggestion in the prior art known to applicant of shutting off a reciprocating refrigerant compressor should liquid accumulate adjacent a valve mechanism which is at the same temperature as the refrigerant gas. It should be stressed that because of the thermodynamics of the working refrigerant fluid, temperature sensing is not adequate, and one must depend upon a state of matter sensor.

While I have described a presently preferred form of the invention, it will be understood by those skilled in the art that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

I claim:

1. In a refrigerant compressor including an outer housing compression mechanismin the housing, cylinder and piston means in said compression mechanism, valve mechanism for controlling the flow of fluid to and from said cylinder and piston means, a sump for lubricant being defined in said housing and power means for actuating the piston means, characterized by the improvement comprising a state of matter sensor disposed adjacent the inlet to the valve mechanism for sensing a predetermined liquid condition at such location and preventing operation of the compressor until such liquid condition has been obviated said valve mechanism including suction valving said power means comprising an electric motor, said state of matter sensor comprising a thermistor secured to the compression mechanism and electrically connected in circuit with the electric motor for detecting the presence of an undesired quantity of liquid at the entrance to the suction valving.

2. A method of controlling the operation of a refrigerant compressor including an outer housing, compression mechanism in the housing, cylinder and piston means in the compression mechanism, valve mechanism for controlling the flow of fluid to and from the cylinder and piston means, a sump for lubricant defined in the housing, and power means comprising an electric motor for actuating the piston means, comprising the steps of actuating the electric motor in response to predetermined temperature conditions in a zone to be treated and preventing operation of the electric motor by sensing a predetermined liquid condition adjacent the inlet to the valve mechanism in the compressor, and permitting operation of the electric motor when such liquid condition has been obviated, thereby preventing damage to the valve mechanism.

3. A method as in claim 2 wherein the compressor includes suction valving and the liquid is sensed at the entrance to said suction valving in the compressor.

4. In a refrigerant compressor including an outer housing, compression mechanism in the housing, cylinder and piston means in said compression mechanism, valve mechanism cooperating with the cylinder and piston means, and power means for actuating the piston means comprising an electric motor, the improvement comprising a state of matter sensor disposed adjacent thefinlet to the valve mechanism for sensing the presence of an undesired quantity of liquid at the inlet to the valve mechanism, and said state of matter sensor being connected in circuit with said electric motor for preventing operation of the electric motor until the presence of the undesired quantity of liquid is no longer sensed.

5. A refrigerant compressor as in claim 4 wherein the state of matter sensor comprises a thermistor connected to the compression mechanism. 

1. In a refrigerant compressor including an outer housing compression mechanism in the housing, cylinder and piston means in said compression mechanism, valve mechanism for controlling the flow of fluid to and from said cylinder and piston means, a sump for lubricant being defined in said housing and power means for actuating the piston means, characterized by the improvement comprising a state of matter sensor disposed adjacent the inlet to the valve mechanism for sensing a predetermined liquid condition at such location and preventing operation of the compressor until suCh liquid condition has been obviated said valve mechanism including suction valving said power means comprising an electric motor, said state of matter sensor comprising a thermistor secured to the compression mechanism and electrically connected in circuit with the electric motor for detecting the presence of an undesired quantity of liquid at the entrance to the suction valving.
 2. A method of controlling the operation of a refrigerant compressor including an outer housing, compression mechanism in the housing, cylinder and piston means in the compression mechanism, valve mechanism for controlling the flow of fluid to and from the cylinder and piston means, a sump for lubricant defined in the housing, and power means comprising an electric motor for actuating the piston means, comprising the steps of actuating the electric motor in response to predetermined temperature conditions in a zone to be treated and preventing operation of the electric motor by sensing a predetermined liquid condition adjacent the inlet to the valve mechanism in the compressor, and permitting operation of the electric motor when such liquid condition has been obviated, thereby preventing damage to the valve mechanism.
 3. A method as in claim 2 wherein the compressor includes suction valving and the liquid is sensed at the entrance to said suction valving in the compressor.
 4. In a refrigerant compressor including an outer housing, compression mechanism in the housing, cylinder and piston means in said compression mechanism, valve mechanism cooperating with the cylinder and piston means, and power means for actuating the piston means comprising an electric motor, the improvement comprising a state of matter sensor disposed adjacent the inlet to the valve mechanism for sensing the presence of an undesired quantity of liquid at the inlet to the valve mechanism, and said state of matter sensor being connected in circuit with said electric motor for preventing operation of the electric motor until the presence of the undesired quantity of liquid is no longer sensed.
 5. A refrigerant compressor as in claim 4 wherein the state of matter sensor comprises a thermistor connected to the compression mechanism. 